1. Field of the Invention
The present invention relates to an ion beam neutralization device for use in an ion beam gun.
2. Description of the Prior Art
Ion beam materials processing systems are known and are used for both ion beam etching and for sputtering. In ion beam etching, an ion emission beam directly impinges the surface of a specimen on which the etching occurs, such as a semiconductor chip provided with an etching mask. In sputtering, a target is placed in the ion emission beam so that material is eroded from the target by the ion beam and the eroded material is sputtered or deposited on a specimen surface. See further R. A. Powell, "Dry Etching for Microelectronics" North Holland Physics Publishing (1984), Page 120, FIG. 5 and Page 137, FIG. 13.
In East German DD Pat. No. 14 66 25, an apparatus for coating and etching substrates is disclosed wherein the coating and etching are promoted by ion emissions. A dc voltage field aids acceleration of the ions, however, the disclosed device does not include a neutralization means. A similar device is disclosed in D. Bolenger "Ion Beam Etching with Reactive Gasses", Solid State Technology (1983), pp. 99-105, particularly FIG. 1, page 100, which includes a neutralization means in the form of a filament in the ion beam. In the disclosed device, the specimen mount lies at a voltage equal to that of the environment.
In Tsukada et al, U.S. Pat. No. 4,399,016, a plasma etching device is disclosed having high-frequency alternating current plasma, but without a neutralization means. In the Tsukada device, the specimen mounts are held at a positive potential and the surface thereof is coated with a dielectric layer. A sample to be etched is placed on the specimen mount and is, thus, insulated from the dc voltage. The specimen and specimen mount are held at the same ac potential due to the capacitance generated by the dielectric layer. Since the specimen charges negatively in the ac plasma, the positive ac potential of the specimen mount serves to hold the specimen in place by means of electrostatic attraction.
Another ion beam apparatus is disclosed in Cuomo et al, U.S. Pat. No. 4,351,712 in which a specimen is affixed to a metallic specimen mount held at environmental potential.
It is known to neutralize the space charge of an ion beam to prevent the beam from expanding by blending negatively charging electrons emitted from an electron source with the positively charged ions. Such an electron source, when used in an ion system, is known as a neutralization means.
Satisfactory operation is not generally achieved in the prior art ion beam processing systems, and particularly in extreme cases such as where a specimen and specimen mount have relatively good electrical conductivity or, respectively, where a target for use in a sputtering process exhibits relatively good electrical conductivity. The use of a neutralization means as disclosed in the prior art has also been attributed to contamination of specimens.